Conventionally, various types of input-and output devices, to which input operation is carried out by an input pen including, for example, a light-emitting element, have been developed as a portable device. In these input and output devices, a large number of sensor sections each including photo-diode are aligned over the surface of a panel, and input operation is carried out by an electromotive force or a resistance change of the photo-diodes receiving light from the input pen. For example, the following documents specifically disclose an arrangement of such an input and output device:
(1) Japanese Laid-Open Patent Application No. 66142/1983 (Tokukaisho 58-66142, published on Apr. 20, 1983);
(2) “Amorphous Silicon Two-Dimensional Image Sensor and its Applications”, ITE Technical Report Vol. 17 No. 16 pp25–30 (published on Mar. 4, 1993);
(3) “Two-Dimensional Contact-type Image Sensor Using Amorphous Silicon Photo-Transistor”, ITE Technical Report Vol. 17 No. 16 pp 19–24 (published on Mar. 4, 1993);
(4) Japanese Laid-Open Patent Application No. 322005/1995 (Tokukaihei 7-322005, published on Dec. 8, 1995); and
(5) Japanese Laid-Open Patent Application No. 302593/1992 (Tokukaihei 4-302593, published on Oct. 26, 1992).
Among the above documents, the input and output devices disclosed in the conventional documents (1) to (4) are arranged so that output voltage from the photo-diode can be taken out and sent to an output line. The following will describe such an arrangement more specifically, for example, with the arrangement described in the conventional document (4).
In the input and output device described in the conventional document (4), as shown in FIG. 16, a source line 101 and a gate line 102 are provided in a matrix manner, and further, a grand line 103 and an input and output switching line 104 are provided in parallel with the gate line 102. TFTs 105 to 107, a photo-diode 108, an auxiliary capacitance 109, and a liquid crystal 110 are provided in a pixel formed in the vicinity of each intersection between the source line 101 and the gate line 102.
A gate terminal of the TFT 105 is connected to the gate line 102, a gate terminal of the TFT 106 is connected to the source line 101 via the TFT 105, and a gate terminal of the TFT 107 is connected to the input and output switching line 104. An anode of the photo-diode 108 is connected to the grand line 103. A cathode of the photo-diode 108 is connected to the source line 101 via the TFTs 105 and 107 and to the gate terminal of the TFT 106 via the TFT 107. One terminal of the auxiliary capacitance 109 is connected to the grand line 103, and the other terminal is connected to the source line 101 via the TFT 105, to the photo-diode 108 via the TFT 107, and to the gate terminal of the TFT 106.
In case where this input and output device operates as a sensor, the TFT 107 is always turned ON by a signal supplied from the input and output switching line 104, photoelectric current produced by the photo-diode 108 is stored in the auxiliary capacitance 109, and voltage of the auxiliary capacitance 109 rises. In this state, the gate line 102 is scanned. When a potential of the gate line 102 switches to High, the TFT 105 turns ON, and the voltage of the auxiliary capacitance 109, i.e. a detection signal of the photo-diode 108 is outputted to the source line 101 via the TFT 105.
Further, in case where the input and output device operates as a display, the TFT 107 is always turned OFF by a signal supplied from the input and output switching line 104 so that the photo-diode 108 cannot influence the display of the pixel. In this state, the gate line 102 is scanned. When the potential of the gate line 102 switches to High, the TFT 105 turns ON. A signal of the source line 101 is maintained by the auxiliary capacitance 109, and when a potential of the auxiliary capacitance 109 causes the TFF 106 to turn ON, the liquid crystal 110 conducts display operation in response to voltage supply from an AC source.
In the conventional arrangement, since the output of the photo-diode 108 is read out as the detection signal, the photo-diode 108 needs a high optical sensitivity so that the input and output device can obtain a high sensitivity in the input detection. The input detection with a high sensitivity is difficult to conduct, and a highly sensitive input and output device is also difficult to arrange.
Further, since output level of-the photo-diode 108 is -low, devices such as an amplifier are necessary to output the output signal of the photo-diode 108 as the detection signal of the input and output device. This makes an arrangement of peripheral devices complex. As a result of this, downsizing of the device, for example, an arrangement of an integrated combination of a driver section including the amplifier and an input and output panel including a sensor section is difficult.
Meanwhile, in the input and output device described in the conventional document (5), as shown in FIG. 17, a data wire (source line) 121 and an address wire (gate line) 122 are provided in a matrix manner. Transistors 123 to 127, photoelectric detecting means 128, and electrostatic capacitances 129 and 130 are provided in a pixel formed in the vicinity of each intersection between the data wire 121 and the address wire 122.
In this input and output device, when the gate line 122 (n+1) is supplied a High level voltage, the transistor 123 turns ON, a gate terminal of the transistor 124 is supplied the High level voltage, thereby turning the transistor 124 ON.
Here, in case where light is not incident to the photoelectric detecting means 128, the transistor 125 remains OFF because the transistor 124 is ON even if the High level voltage is supplied to the address wire 122n. Moreover, although the transistor 126 turns ON, voltage is not outputted to the data wire 121 because of the transistor 125 being OFF.
On the other hand, when light is incident to the photoelectric detecting means 128, the High level voltage applied from the address wire 122 (n+1) to the gate terminal of the transistor 124, being influenced by output from the photoelectric detecting means 128, is changed to a Low level voltage. As a result of this, the transistor 124 is switched from ON to OFF. Then, when the High level voltage is supplied to the address wire 122n, a node 131 has a voltage close to the High level voltage, so that the transistor 125 is switched from OFF to ON, and a node 132 has the High level voltage. Moreover, since the transistor 126 turns ON, the High level voltage is outputted to the data wire 121.
In such an arrangement of the conventional document (5), not the output of the photoelectric detecting means 128, but the High level voltage of the address wire 122 is read out as the detection signal to the data wire 121. Therefore, since the detection signal obtained from the data wire 121 is High level, the input and output device needs no devices for amplifying the detection signal, such as an amplifier, so that it is possible to simplify an arrangement of peripheral devices.
However, in the arrangement of the conventional document (5), High level voltage of the address wire 122, which is read out as the detection signal to the data wire 121, has an extremely high value, for example, +15V. For this reason, for example, a reading circuit of the detection signal, which is provided in a driver circuit of the data wire 121, needs to withstand a high voltage.
Further, in the arrangement of the conventional document (5), to turn the transistor 124 OFF, the output of the photoelectric detecting means 128 is used, and voltage of a node 133 (the gate terminal of the transistor 124) is set in Low level to oppose the High level voltage supplied from the address wire 122 (n+1). Therefore, in order to ensure the transistor 124 to be OFF, the photoelectric detecting means 128 needs a high optical sensitivity. This arises a problem that realization of the input and output device is difficult, or the input and output device costs high to manufacture, if realized.